Methods and Findings in Experimental and Clinical Pharmacology
Vol. 25, Suppl. A, 2003
ISSN 0379-0355
Copyright 2003 Prous Science, S.A.
CCC: 0379-0355/2003
http://www.prous.com

High Throughput Screening as a Tool for the Lead Finding Process

T. Doménech

Almirall Prodesfarma, Barcelona, Spain

High throughput screening (HTS) is the process of screening large numbers of compounds against disease targets in order to identify biologically active compounds. As the number of both targets and compounds (libraries) available for screening increase, there is a need to consider methods for making this process more efficient. The goal of HTS is to accelerate drug discovery by screening large libraries often composed of hundreds of thousands of compounds (drug candidates) through a combination of automation (modular or integrated robotics), miniaturization of relevant assays and management of the data generated by these assays.

Lead finding libraries can be designed with concepts of synthetic or structural novelty as a core attribute of the library or they can be designed with concepts of known or hypothesized biological pharmacophores as a central theme. These libraries are synthesized and then screened in assay systems in order to find compounds that "hit" in an assay (hit finding process). Once these hits are found and well characterized (lead finding process), their structure is optimized to provide compounds that possess desirable pharmacological properties (lead optimization process).

Libraries in large pharma companies have grown to include millions of compounds. Each compound has to be stored, preserved, tracked and retrieved. The compound handling process is simplified if compounds are stored in well defined locations that are consistent with a microplate format. Compounds for screening are usually prepared as solutions in DMSO at a high concentration (1-10 mg/ml). By assigning every well plate a unique ID code, compounds can be tracked within the chemical library by plate ID and well location. Compound management needs a specific software capable to save and update all the compound or plate history.

A generic HTS operation consists of four stages: assay set-up and validation, data capture, data analysis and data reporting.

The type of assays for a lead finding process must be amenable to automation. Many technologies such as SPA, TRF, HTRF, FP, Flashplates, etc., are currently employed for high-throughput screening to help to transform manual to automated assay. Screeners define assays as either heterogeneous or homogeneous. Heterogeneous assays require steps that go beyond simple fluid additions, incubations and reading (e.g., filtration, centrifugation, and plate washing steps). Homogeneous assays require only additions and incubations followed by reading. Despite the advantages of homogeneous assays (easy to perform and automatic), we still use heterogeneous assays in HTS. Miniaturization of assays involves increasing the density of microwells in microplates while decreasing their volume (96, 394, 1536...wells/plate). This helps to reduce cost and time for lead finding process.

Assay results need to be collected and stored in databases. Experimental data capture involves calculation set-up, plate set-up and compound tracking. Commercial software such as Activity Base (IDBS) is available for this purpose. Tools like Spotfire have also been developed to visualize the results using interactive and graphical representations to help identify plate patterns, outliers, assay drifts, etc. Following this, data are validated and reporting of data is achieved through effective querying and report generation tools.

Automation technologies have significantly modified the drug discovery process during the past two decades, especially in small volume liquid pipetting, reliable handling of standardized plates, simplified assay formats and data management. Automation technologies will continue to improve the drug discovery process in the future, but in new ways and with a broader set of goals.

Methods and Findings in Experimental and Clinical Pharmacology Vol. 25, Suppl. A, 2003
ISSN 0379-0355 Copyright 2003 Prous Science, S.A. CCC: 0379-0355/2003 http://www.prous.com